阴极界面修饰层改善平面p-i-n型钙钛矿太阳能电池的光伏性能

有机/无机杂化金属卤化物钙钛矿半导体材料结合了有机材料良好的溶液可加工性以及无机材料优越的光电特性,近几年受到了热捧,成为太阳能电池领域一颗耀眼的明星. 伴随着钙钛矿薄膜结晶过程和形貌的优化、器件结构的改进以及电极界面材料的开发,这类有机/无机杂化金属卤化物钙钛矿太阳能电池的光电转换效率从最初的3.8%迅速提高到目前最高的22.1%. 其中界面工程在提升器件性能上发挥着极其重要的作用. 本文总结了平面p-i-n型钙钛矿太阳能电池中阴极界面修饰层（CBL）的研究进展. CBL从材料上讲可分为无机金属氧化物、金属或金属盐以及有机材料,从构成上讲可分为单层CBL、双层CBLs以及共混型CBL. 本文对这些类型的CBL分别给予详细的介绍. 最后,我们归纳出CBL在改善器件效率和稳定性上所起的作用以及理想CBL所应满足的要求,希望能为以后阴极界面修饰材料的设计提供一定的借鉴.     

Aqueous Synthesis of Methylammonium Lead Halide Perovskite Nanocrystals

Methylammonium lead halide perovskite nanocrystals offer attractive optoelectronic properties but suffer from fast degradation in the presence of water. In contradiction to this observation, we demonstrate the possibility of a direct aqueous synthesis of CH₃NH₃PbX₃ (X=Br or Cl/Br) nanocrystals through the reaction between the lead halide complex and methylamine when the pH is maintained in the range of 0–5. Under these synthetic conditions, the positively charged surface of the perovskite nanocrystals and the proper ionic balance help to prevent their decomposition in water. Additional surface capping with organic amine ligands further improves the photoluminescence quantum yield of the perovskite nanocrystals to values close to 40 %, ensures their stability under ambient conditions for several months, and their photoluminescence performance under continuous 0.1 W mm^?2 405 nm light irradiation for over 250 hours.     

Composition-Controlled Synthesis of Hybrid Perovskite Nanoparticles by Ionic Metathesis: Bandgap Engineering Studies from Experiments and Theoretical Calculations

Herein a newly discovered non-polar solvent based synthesis of MAPbX₃ hybrid perovskite nanoparticles (NPs) is presented, where MA=Methylammonium and X=I, Br and Cl, as well as their mixed halide counterparts. The methodology proposed is simple and uses low-cost commercial precursors. The conventional method of hybrid perovskite preparation requires methylammonium halide precursors and highly polar solvents. Mandatory use of polar solvents and a particular perovskite precursor makes an intermediate compound which then requires a non-polar solvent to recover the NPs. In contrast here, a whole range of mixed halide perovskite NPs is fabricated without using a methylammonium halide precursor and a polar solvent. In this method, a non-polar solvent is used, which provides a better platform for the particle recovery. Organic cations on the nanoparticle surface prevent degradation from water, due to their hydrophobic nature, and hence offer a stable colloidal suspension in toluene for more than three months. Ab-initio calculations within density functional theory (DFT) predict lower formation energies compared to previously reported values, confirming better chemical stability for this synthesis pathway. Through the halide compositional tuning, these NPs exhibit a variety of emission and absorption starting from ultraviolet to near infrared (IR). The absorption spectra of various halide perovskite show a sharp band edge over the visible wavelength with high absorption coefficient. High oscillator strengths due to high excitonic binding energies combined with the simulated finite dipole transition probabilities point towards the observed high absorption. The emission spectra of mixed halide perovskites vary from 400 to 750 nm, which covers the whole range of visible spectra with sharp full-width at half maxima. Different halide perovskite exhibit average recombination lifetime from 5 to 227 ns. Ambient synthesis, chemical robustness and tunability of emission with varying halide compositions make MAPbX₃ (X=I, Br and Cl) NPs appealing for the optoelectronic applications.     

反溶剂法快速合成高效发光二维锡卤钙钛矿材料

铅卤钙钛矿材料由于其优异的光电性质而受到了广泛关注. 但是, 材料中铅的毒性问题极大地阻碍了其大规模应用. 因此, 寻找与铅卤钙钛矿具有相似光电性质的非铅卤化物钙钛矿材料十分重要. 其中, 锡基卤化物钙钛矿被认为是铅基钙钛矿材料最佳的替代材料之一. 本文通过简便的反溶剂方法, 合成了一系列新型二维(RNH₃)₂SnX₄(R为烷基链, X=Br^-, I^-)钙钛矿材料. 研究结果表明, 所合成的材料具有优异的荧光发射性质, 发光量子效率高达98.5%, 比三维ASnX₃[A=Cs⁺, 甲胺(MA⁺), 甲脒(FA⁺)等]型钙钛矿表现出更好的稳定性. 本文所采用的合成方法简单易行, 有利于实现金属卤化物钙钛矿材料的大规模合成及在固态照明器件和显示器件领域的工业应用.     

Facile method for synthesis of mixed-cation halide perovskites by mild equilibrium conversion via iodine-mediated transport reaction in inert liquid media

A new facile method for the synthesis of mixed-cation halide R2 = 0.9935 perovskites based on the chemical conversion of solid precursors (organic halides and lead halides) via an iodine-mediated transport reaction in inert liquid media under mild conditions is described. The equilibrium nature of the conversion provides an exact match between the stoichiometry of the resulting perovskite powder and the molar ratio of the precursors. This method can serve as a useful tool for the synthesis of complex perovskite precursors and the investigation of phase equilibria     

钙钛矿材料光催化还原CO2综述

利用半导体材料光催化还原CO2合成可燃物是目前解决能源危机和缓解温室效应的理想途径.本文对几种钙钛矿型材料,包括纯无机卤化物钙钛矿材料、金属有机钙钛矿材料、氧化物型钙钛矿材料和复合型钙钛矿材料在光催化还原CO2领域的应用进行了简单的归纳与总结.     

Lead‐Free Halide Perovskite Nanocrystals: Crystal Structures,Synthesis, Stabilities,and Optical Properties

In recent years, there have been rapid advances in the synthesis of lead halide perovskite nanocrystals (NCs) for use in solar cells, light emitting diodes, lasers, and photodetectors. These compounds have a set of intriguing optical, excitonic, and charge transport properties, including outstanding photoluminescence quantum yield (PLQY) and tunable optical band gap. However, the necessary inclusion of lead, a toxic element, raises a critical concern for future commercial development. To address the toxicity issue, intense recent research effort has been devoted to developing lead‐free halide perovskite (LFHP) NCs. In this Review, we present a comprehensive overview of currently explored LFHP NCs with an emphasis on their crystal structures, synthesis, optical properties, and environmental stabilities (e.g., UV, heat, and moisture resistance). In addition, strategies for enhancing optical properties and stabilities of LFHP NCs as well as the state‐of‐the‐art applications are discussed. With the perspective of their properties and current challenges, we provide an outlook for future directions in this rapidly evolving field to achieve high‐quality LFHP NCs for a broader range of fundamental research and practical applications.     

Engineering of CH3NH3PbI3 Perovskite Crystals by Alloying Large Organic Cations for Enhanced Thermal Stability and Transport Properties

The number of studies on organic–inorganic hybrid perovskites has soared in recent years. However, the majority of hybrid perovskites under investigation are based on a limited number of organic cations of suitable sizes, such as methylammonium and formamidinium. These small cations easily fit into the perovskite's three‐dimensional (3D) lead halide framework to produce semiconductors with excellent charge transport properties. Until now, larger cations, such as ethylammonium, have been found to form 2D crystals with lead halide. Here we show for the first time that ethylammonium can in fact be incorporated coordinately with methylammonium in the lattice of a 3D perovskite thanks to a balance of opposite lattice distortion strains. This inclusion results in higher crystal symmetry, improved material stability, and markedly enhanced charge carrier lifetime. This crystal engineering strategy of balancing opposite lattice distortion effects vastly increases the number of potential choices of organic cations for 3D perovskites, opening up new degrees of freedom to tailor their optoelectronic and environmental properties.     

All‐Inorganic CsPbX3 Perovskite Solar Cells: Progress and Prospects

Recently, lead halide‐based perovskites have become one of the hottest topics in photovoltaic research because of their excellent optoelectronic properties. Among them, organic‐inorganic hybrid perovskite solar cells (PSCs) have made very rapid progress with their power conversion efficiency (PCE) now at 23.7 %. However, the intrinsically unstable nature of these materials, particularly to moisture and heat, may be a problem for their long‐term stability. Replacing the fragile organic group with more robust inorganic Cs⁺ cations forms the cesium lead halide system (CsPbX₃, X is halide) as all‐inorganic perovskites which are much more thermally stable and often more stable to other factors. From the first report in 2015 to now, the PCE of CsPbX₃‐based PSCs has abruptly increased from 2.9 % to 17.1 % with much enhanced stability. In this Review, we summarize the field up to now, propose solutions in terms of development bottlenecks, and attempt to boost further research in CsPbX₃ PSCs.     

Hole‐Transport Materials for Perovskite Solar Cells

The pressure to move towards renewable energy has inspired researchers to look for ideas in photovoltaics that may lead to a major breakthrough. Recently the use of perovskites as a light harvester has lead to stunning progress. The power conversion efficiency of perovskite solar cells is now approaching parity (>22 %) with that of the established technology which took decades to reach this level of performance. The use of a hole transport material (HTM) remains indispensable in perovskite solar cells. Perovskites can conduct holes, but they are present at low levels, and for efficient charge extraction a HTM layer is a prerequisite. Herein we provide an overview of the diverse types of HTM available, from organic to inorganic, in the hope of encouraging further research and the optimization of these materials.     

Supramolecular Coordination of Pb2+ Defects in Hybrid Lead Halide Perovskite Films Using Truxene Derivatives as Lewis Base Interlayers

Truxene derivatives, due to their molecular structure and properties, are good candidates for the passivation of defects when deposited onto hybrid lead halide perovskite thin films. Moreover, their semiconductor characteristics can be tailored through the modification of their chemical structure, which allows-upon light irradiation- the interfacial charge transfer between the perovskite film and the truxene molecules. In this work, we analysed the use of the molecules as surface passivation agents and their use in complete functional solar cells. We observed that these molecules reduce the non-radiative carrier recombination dynamics in the perovskite thin film through the supramolecular complex formation between the Truxene molecule and the Pb²⁺ defects at the perovskite surface. Interestingly, this supramolecular complexation neither affect the carrier recombination kinetics nor the carriers collection but induced noticeable hysteresis on the photocurrent vs voltage curves of the solar cells under 1 sun illumination.     

Visible‐Light‐Promoted Trifluoromethylthiolation of Styrenes by Dual Photoredox/Halide Catalysis

Herein, we report a new visible‐light‐promoted strategy to access radical trifluoromethylthiolation reactions by combining halide and photoredox catalysis. This approach allows for the synthesis of vinyl–SCF₃ compounds of relevance in pharmaceutical chemistry directly from alkenes under mild conditions with irradiation from household light sources. Furthermore, alkyl–SCF₃‐containing cyclic ketone and oxindole derivatives can be accessed by radical‐polar crossover semi‐pinacol and cyclization processes. Inexpensive halide salts play a crucial role in activating the trifluoromethylthiolating reagent towards photoredox catalysis and aid the formation of the SCF₃ radical.     

Facile low-temperature solid-state synthesis of efficient blue-emitting Cs3Cu2I5 powder phosphors for solid-state lighting

The discovery of new environmentally friendly luminescent materials with high photoluminescence quantum yield and long-term stability is critical for future solid-state lighting and displays applications. Although lead halide perovskite materials with excellent optical properties have been extensively investigated in recent years because they hold tremendous promise in optoelectronic devices, the toxicity of lead and poor air-stability still hinder their commercial applications. Moreover, while substantial work has been done on three-dimensional (3D) perovskite halides, the zero-dimensional (0D) halide emitters with bright luminescence remain elusive. Herein we report a facile solid-state reaction method to prepare an efficient lead-free all-inorganic halide material with 0D structure, Cs₃Cu₂I₅, with photoluminescence quantum yield up to 80%. Under ultraviolet excitation at 313 nm, the Cs₃Cu₂I₅ powder phosphors show a strong blue photoluminescence emission with peak at 445 nm and CIE color coordinates of (0.1486, 0.0873). Notably, Cs₃Cu₂I₅ exhibits good color stability at high temperatures and outstanding stability towards air exposure exceeding one month (30 days). These findings not only open up a door for the development of promising highly emissive low-dimensional halide materials for lighting and displays, but also offer a new scalable approach for the potential mass production of halide emitters.     

Synthesis of Layered Carbonitrides from Biotic Molecules for Photoredox Transformations

The construction of layered covalent carbon nitride polymers based on tri-s-triazine units has been achieved by using nucleobases (adenine, guanine, cytosine, thymine and uracil) and urea to establish a two-dimensional semiconducting structure that allows band-gap engineering applications. This biomolecule-derived binary carbon nitride polymer enables the generation of energized charge carrier with light-irradiation to induce photoredox reactions for stable hydrogen production and heterogeneous organosynthesis of C−O, C−C, C−N and N−N bonds, which may enrich discussion on chemical reactions in prebiotic conditions by taking account of the photoredox function of conjugated carbonitride semiconductors that have long been considered to be stable HCN-derived organic macromolecules in space.     

Accelerated Interfacial Charge Transfer in Br-Gradient MAPbI3-xBrx Perovskite Thin Films?

Mixed halide perovskites (MHPs) are a class of semiconductor materials with great promise for many optoelectronic applications due to their outstanding photophysical properties. Understanding and tailoring the photogenerated carrier dynamics is essential for further improvement of perovskite performance. Herein, we report a study about the carrier transport and interfacial charge transfer dynamics in Br-gradient MAPbI_3-xBr_x perovskite thin films prepared by surface ion-exchange method. Driven by the bandgap gradient in MAPbI_3-xBr_x films, the accelerated internal hole transport and enhanced interfacial extraction efficiency were both observed. Meanwhile, the interfacial electron transfer was also found to be evidently facilitated due to the surface modification during post-treatment. Our findings suggest the possibility of simultaneous acceleration of interfacial electron and hole transfer processes in halide perovskite films via surface post-treatment technique, which is of great importance in further improving the power conversion efficiency of perovskite solar cells.     

Completely Amine-Free Open-Atmospheric Synthesis of High-Quality Cesium Lead Bromide (CsPbBr3) Perovskite Nanocrystals

Cesium lead halide perovskite nanocrystals (NCs) CsPbX₃ (X=Cl, Br, and I) have been prominent materials in the last few years due to their high photoluminescence quantum yield (PLQY) for light-emitting diodes and other significant applications in photovoltaics and optoelectronics. In colloidal CsPbX₃ synthesis, the most commonly used ligands are oleic acid and oleylamine. The latter plays an important role in surface passivation but may also be responsible for poor colloidal stability as a result of facile proton exchange leading to the formation of labile oleylammonium halide, which pulls halide ions out of the NC surface. Herein, a facile, efficient, completely amine-free synthesis of cesium lead bromide perovskite nanocrystals using hydrobromic acid as halide source and tri-n-octylphosphane as ligand under open-atmospheric conditions is demonstrated. Hydrobromic acid serves as labile source of bromide ion, and thus this three-precursor approach (separate precursors for Cs, Pb, Br) gives more control than a conventional single-source precursor for Pb and Br (PbBr₂). The use of HBr paved the way to eliminate oleylamine, and thus the formation of labile oleylammonium halide can be completely excluded. Various Cs:Pb:Br molar ratios were studied and optimum conditions for making very stable CsPbBr₃ NCs with high PLQY were found. These completely amine-free CsPbBr₃ perovskite NCs synthesized under bromine-rich conditions exhibit good stability and durability for more than three months in the form of colloidal solutions and films, respectively. Furthermore, stable tunable emission across a wide spectral range through anion exchange was demonstrated. More importantly, this work reports open-atmosphere-stable CsPbBr₃ NCs films exhibiting strong PL, which can be further used for optoelectronic device applications.     

Porous and Water Stable 2D Hybrid Metal Halide with Broad Light Emission and Selective H2O Vapor Sorption

In this work we report a strategy for generating porosity in hybrid metal halide materials using molecular cages that serve as both structure-directing agents and counter-cations. Reaction of the [2.2.2] cryptand (DHS) linker with Pb^II in acidic media gave rise to the first porous and water-stable 2D metal halide semiconductor (DHS)₂Pb₅Br₁₄. The corresponding material is stable in water for a year, while gas and vapor-sorption studies revealed that it can selectively and reversibly adsorb H₂O and D₂O at room temperature (RT). Solid-state NMR measurements and DFT calculations verified the incorporation of H₂O and D₂O in the organic linker cavities and shed light on their molecular configuration. In addition to porosity, the material exhibits broad light emission centered at 617 nm with a full width at half-maximum (FWHM) of 284 nm (0.96 eV). The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens new pathways towards unexplored applications (e.g. solid-state batteries) for this class of hybrid semiconductors.     

The Significance of Ion Conduction in a Hybrid Organic–Inorganic Lead‐Iodide‐Based Perovskite Photosensitizer

The success of perovskite solar cells has sparked enormous excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such crystalline absorber materials. Far from being exhaustively studied in terms of solid‐state properties, these materials surprised by anomalies such as a huge apparent low‐frequency dielectric constant and pronounced hysteretic current–voltage behavior. Here we show that methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of iodine ions. In particular, we measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build‐up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into electrical charge transport in the hybrid organic–inorganic lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder.     

Stabilizing the black phase of cesium lead halide inorganic perovskite for efficient solar cells

Inorganic perovskite cesium lead halide is extensively studied because of its potential in improving the thermal stability of perovskite materials. However, the tolerance factor of this type of perovskite is near the critical value, which leads to phase instability. The optoelectronic active black phases(α, β, and γ phases of CsPbI_3) are metastable at room temperature, which can be easily transferred into an optoelectronic inactive yellow phase(δ-CsPbI_3). This review highlights recent progress in stabilizing the black phase for efficient and stable perovskite solar cells.     

金属卤化物钙钛矿纳米晶高效发光二极管的制备与器件性能优化

金属卤化物钙钛矿作为一类新型的离子型直接带隙半导体材料在电致发光二极管(LED)中有着重要应用前景. 但实现其应用的前提在于金属卤化物钙钛矿材料需要保持高的发光效率和好的稳定性. 为了提高金属卤化物钙钛矿作为LED发光层的激子结合效率, 从而提升其发光效率, 设计和合成金属卤化物钙钛矿纳米晶材料是一个有效途径. 目前, 基于纳米晶材料设计的金属卤化物钙钛矿LED在绿光和红光(包括近红外光)范围已经展现了高的发光亮度和外量子效率(EQE), 其中最高EQE已经超过了20%, 但其稳定性仍无法满足器件应用的要求. 此外, 更值得关注且更重要的是, 蓝光钙钛矿LED的发光亮度和EQE目前仍然不高. 如何制备高效、 稳定的金属卤化物钙钛矿纳米晶LED, 特别是蓝光LED, 是一个具有重大应用前景且具有挑战性的课题. 本文重点介绍了金属卤化物钙钛矿纳米发光层的结构设计和合成方法及金属卤化物钙钛矿LED的研究进展, 分析了金属卤化物钙钛矿LED不稳定的原因, 并对金属卤化物钙钛矿LED研究面临的挑战和未来发展方向进行了总结与展望.